The names Corispermum hyssopifolium and C. villosum have been misapplied to C. welshii. Judging from its fruit morphology, C. welshii is closely related to C. americanum, especially to var. rydbergii. Forms intermediate between these taxa occasionally occur, especially in Utah. However, C. welshii differs from C. americanum in having shorter and thicker inflorescences and broader leaves and bracts. Forms similar to C. welshii occur also in other southwestern states, particularly in Colorado and western Texas. These plants are in need of additional study.